This invention relates to an improved direction-finding system and method utilizing detection by underwater listening, radio frequency or microwave detection in air or transduction of other electro-magnetic energy of a character permitting suitable time delay of signal intelligence.
Prior detection systems for listening have incorporated the comparison of nulling signals obtained from at least a pair of microphones of a detection array system by connection thereof either in series opposition to provide a subtractive output, or by connection thereof in a series aiding relationship to provide an additive comparison. The subtractive and additive outputs of the two arrangements may thereafter be compared to obtain the direction indication. These prior systems have presented certain shortcomings in that ambient noise intelligence which is present in the signals of each of the microphones, or hydrophones in the case of underwater placement thereof, tends to mask the nulling signal and the desired signal intelligence indication obtained by nulling is only valid to the extent that it shows a null down to the background level in the case of a subtractive system or shows the value of the nulling signal plus the background signal in an additive comparison system. Also these prior detection systems, whether they use a pair of individual microphones or a system utilizing an array of microphones combined in an overall or composite pair, tend to pick up interferring noises and indicate additional null points as the hydrophones of the array are swung or effectively swung about a central base point of ranging. This makes it difficult to discriminate between spurious and desired sound sources. Further difficulty is frequently encountered where attempts are made to analyze the information obtained by such nulling methods to determine if the primary signal source produced a certain null or whether the null was produced by wave lengths of other frequencies originating in the same general direction as the noise source of interest.